Process for the preparation of a concentrate of metals, rare metals and rare earth metals from residues of alumina production by bayer process or from materials with a chemical composition similar to said residues, and refinement of the concentrate so obtained

ABSTRACT

The sole FIGURE appended shows the simplified block diagram of the invention, in terms of its most extensive definition.

This invention relates to the technical field of the recovery of metals,rare metals and rare earth metals from residues produced during theproduction of alumina by the Bayer process (known as “red mud”).

More specifically, the invention relates to the extraction of scandium,yttrium, lanthanum, aluminium, iron, titanium, gallium and any othermetals, rare metals and rare earth metals present in the so-called redmud, which is a side-product obtained during the Bayer process for theextraction of alumina from bauxite.

The process, in its entirety, according to the invention results in theformation of a concentrate containing the elements of interest and thesubsequent selective separation of compounds containing the elements ofinterest. The entire process is conceived in such a way as to transforma waste to be disposed of in landfill into a series of products whichcan be reused in the Bayer process or which can be re-inserted in thereference markets, without producing further waste, thus following theprinciples of zero waste and circular economy. The invention thereforehas a strong economic and ecological importance.

As is known, the industrial process most commonly used to obtain aluminafrom bauxite is called Bayer process. The main steps which characterizethe process are:

-   -   grinding of the bauxite;    -   digestion of the bauxite in a 10% aqueous solution of NaOH. The        hot solubilization of the alumina present in the bauxite occurs        during this step. The temperatures during this step can range        from approximately 150° C. (solubilization of trihydrate        alumina) to 250° C. with a high reaction pressure (for the        solubilization monohydrate alumina);    -   separation of the insolubles (red mud) by decantation and        filtration;    -   precipitation of Al(OH)₃ by lowering the temperature;    -   calcination of Al(OH)₃, to obtain anhydrous alumina, Al₂O₃.

Although the exact composition of the bauxites used for the productionof alumina with the Bayer process can differ according to the mine oforigin, they all contain oxides of Al, Ti, Fe and Si in variouscompositions and percentages; moreover, there are traces of otherelements such as zinc, vanadium and some rare and rare earth metals. Theextraction efficiency of the Bayer process is very low and this resultsin the presence of large quantities of metallic elements in theprocessing waste, generally called “red mud”.

Table 1 indicates a typical composition of a red mud produced by theBayer process.

TABLE 1 main components of red mud Unit of Parameter measurement ValuesAl₂O₃ % 16-18 Fe₂O₃ % 51-57 TiO₂ % 3-5 SiO₂ %  8-12 Na₂O % 4-6 CaO %0.03-2.30 V₂O₅ % 0.14-0.21 MgO % 0.13-0.18 MnO % 0.157-0.250 LOI at1000° C. % 11-13

Table 2 shows the trace elements and the rare earths present in a NALCOred mud.

TABLE 2 trace elements and rare earths in red mud Unit of Parametermeasurement Values Sc mg/kg 69.97 V mg/kg 746.35 Cr mg/kg 846.38 Comg/kg 22.14 Ni mg/kg 45.91 Cu mg/kg 103.86 Zn mg/kg 86.57 Ga mg/kg 93.17Rb mg/kg 5.99 Sr mg/kg 47.66 Y mg/kg 9.94 Zr mg/kg 234.13 Nb mg/kg 40.07Cs mg/kg 0.25 Ba mg/kg 90.77 Hf mg/kg 8.28 La mg/kg 42.06 Ce mg/kg 95.96Pr mg/kg 7.16 Nd mg/kg 18.65 Sm mg/kg 3.36 Eu mg/kg 0.83 Gd mg/kg 3.48Tb mg/kg 0.33 Dy mg/kg 2.10 Ho mg/kg 0.29 Er mg/kg 0.82 Tm mg/kg 0.13 Ybmg/kg 0.99 Lu mg/kg 0.14

In addition to the above-mentioned characteristics, red muds, if theyare not neutralized, have an extremely basic pH (approx. pH 12.5).

The red muds are diluted, so that they can be more easily pumped, andare sent to a pressure filter, where some components are recovered;then, in the form of sludge, they are pumped away from the plant to bedisposed of in disposal basins, similar to artificial lagoons. Thispractice has a significant environmental impact since these wastes arenot disposed of efficiently and an industrial application has still notbeen found which is able to absorb the considerable quantity of materialproduced each year.

Red muds therefore potentially have extremely significant impacts, themanagement of which still currently constitutes a serious problem. Eventhough the red muds are currently managed in such a way as to minimizethe impacts, they still represent an enormous hazard for human health;moreover, some sites still feel the effects of an incorrect managementin the past. The surface deposits where the red muds are stored must beconstructed and managed with particular care to avoid contamination ofthe ground water and the surrounding soils and to prevent dusty materialfrom being dispersed into the air, thus causing harmful effects for thehealth; in fact, these dusts are of an extremely alkaline nature andcause irritation of the skin, eyes and the respiratory system.

Numerous studies and trials have been promoted over recent years toidentify an adequate treatment of these wastes. In some cases, the highcontent of aluminium in the material has led to the modification of theproduction cycle in order to reduce the alkaline load, so as to obtainan inert mud which can be used to cover mines that are no longer used asa sub-stratum for planting the original vegetation or for otheragricultural purposes or as backfill material for coastal areas. Lastly,the use of red muds has also been tested in the production ofconstruction materials.

On the other hand, the bauxite in the Bayer process contains, as well asthe main elements indicated above, also compounds containing rare andrare earth metals, which can be potentially exploited but theconcentration of which is too low to promote an economically sustainableextraction process.

The type and concentration of the rare and rare earth metals presentvaries according to the type of bauxite used; however, amongst thosewith the highest concentration there is, for example, gallium andscandium. Due to the effect of the extraction of the alumina during theBayer process, these rare and rare earth metals are also concentrated inthe red muds produced, with the result of reaching concentration valueswhich, even though they are still very low, are sufficient to encouragean extraction process. The typical composition data of a red mud isshown in Tables 1 and 2 above. More specifically, even only theexploitation of the scandium and gallium present could, hypothetically,economically support an extraction process, however their concentrationin the red mud, as that of the other metals, rare metals and rare earthmetals rare present is not yet optimum for rendering their extractioneconomically sustainable. It is therefore necessary to determineenrichment processes which create “concentrates” of the elements ofinterest, in order to overcome this qualitative deficit.

Summing up, even though possible alternative paths have been studied forthe management of red muds, they are still considered to be wastes witha high environmental impact, the treatment and/or disposal of whichrepresents an enormous cost for society. In addition, the depletion ofthe available landfill sites constitutes a problem for the continuationof industrial activities: due to the so-called “NIMBY” (Not In My BackYard) effect, not only in Europe and in the USA, but also in many of theemerging economic powers, the disposal in landfills is seen as the lastoption, after having implemented the so-called 3 R (Reduce, Reuse,Recycle) principle. Consequently, concessions for new landfill sites areincreasingly difficult to obtain.

Therefore, in the specific sector, there is the need to manage red mudswith a more advantageous process in both economic and ecological terms.

The need is satisfied by the process according to this invention, whichalso achieves further advantages which are apparent in the descriptionwhich follows.

The process, as a whole, allows the elements of interest present in thered muds to be concentrated in smaller fractions, having a chemicalcomposition and physical state such as to render technologically easytheir further separation and refinement. The final products produced canbe sent to the start of the Bayer process or sold on the referencemarkets.

This invention therefore relates specifically to a process in which themetals, rare metals and rare earth metals present in the powderyby-products coming from the processing of the bauxite (red muds) areconcentrated, through a multistage process, until reaching values suchas to allow an extraction and separation which is industriallyefficient. The invention also relates to the process for separating theelements of interest, through a multistage process, transforming theminto single products to be re-used in the Bayer process and/or sendingthem to the respective reference markets.

The process is divided into the following passages.

First Concentrating Step, by Separating Occurring Iron:

-   -   optional grinding and drying of the material to be treated        material at a temperature from 60 to 250° C.;    -   optional roasting, in order to also eliminate the        crystallization water;    -   optional grinding of the product dried or subjected to roasting;    -   mixing with components which are able to modify the basicity        index of the mixture, by the addition of SiO₂, MgO₂, CaO or        silica sand. The basicity index is a fundamental parameter for        determining the behaviour of a mineral matrix, or the like,        during the melting processes. In its quaternary form, the        basicity index can be expressed with the following formula:

${IB}_{4} = \frac{\left( {\% {CaO}} \right) + \left( {\% {MgO}} \right)}{\left( {\% {SiO}_{2}} \right) + \left( {\% {Al}_{2}O_{3}} \right)}$

The basicity index, in the conditions of the melting process inquestion, can vary from 0.1 a 2.0, according to the type of red mud tobe treated.

With the variation in the content of calcium, magnesium, silicon andaluminium oxides, there can be variations, for example, in the meltingtemperature, the modes of separation of some phases during the meltingprocess, and their chemical composition.

In this invention, unlike the prior art processes on red muds, theaddition of the components necessary to modify the basicity index of themixture is achieved by adding in suitable proportions a waste comingfrom other processes, known as “fly ash”.

In a preferred application, these fly ashes come from the combustion ofcoal (Coal Fly Ash) and have the further advantages of containing, inturn, rare and rare earth metals.

The following table summarises the typical values for the maincomponents in a coal fly ash:

TABLE 3 Range of composition, shown in the literature, of the maincomponents present in coal fly ash. It should be noted that the elementsare expressed as oxides, due to the analytical technique used (XRFspectrometry) Unit of Parameter measurement Values SiO₂ % 30-55 Al₂O₃ % 4-27 Fe₂O₃ % 4.5-9   MgO % 1.2-6   CaO % 1.2-30  Na₂O % 0.1-1.5 K₂O %0.19-3.5  TiO₂ % 0.6-2.2 P₂O₅ % 0.1-1.0 MnO % 0.06-0.3  Cr₂O₃ %0.01-0.04 Total C % 0.14-25.5 Total S % 0.17-2.8 

-   -   mixing with components which are able to add a potential        reducing agent, by means of the presence of carbon; if Coal Fly        Ash is used, this contains a significant percentage of carbon,        so it also contributes towards providing the opportune reducing        agent;    -   melting of the material, if necessary pre-treated as indicated        above, by means of any of the prior art techniques, in a        suitable reactor, for example a rotary furnace, which is able to        guarantee an operating temperature of the melting bath equal to        or greater than 1300° C. In a preferred embodiment the reactor        can be of the type EAF (Electric Arc Furnace), of the type        plasma transferred arc, plasma not transferred arc, microwave        plasma, Brown's gas reactor and electrolysis catalysed gas        reactor;    -   production of a product enriched in aluminium, titanium and        other metals, rare metals and rare earth metals (slag);    -   simultaneous separation of the iron, with production of a molten        metallic product of poor quality equivalent to pig iron.

At the end of the first concentrating step the rare and rare earthmetals present are drawn into the fraction operatively indicates as“slag”, which is subjected to the subsequent operations. The metalliciron produced, which is of poor quality, equivalent to a pig iron, maybe directed to the reference markets.

Second Concentrating Step (Alternative A), by Separating CompoundsContaining Aluminium and Silicon:

-   -   the slag exiting from the melting in the first concentrating        step is sent directly to a subsequent reactor in which an        alkaline salt or alkaline earth metal of a carbonate is added.        The slag must remain in the liquid state until the reaction with        the carbonate, so its initial temperature will be approximately        1500° C.; after the mixing with the carbonate, the temperature        is lowered to 1000° C. and, continuing with a controlled        cooling, is lowered to temperatures of less than 500° C. The aim        of these actions is to obtain a poorly aggregated matrix, in the        form of powder, exploiting the phenomenon of the so-called        self-disintegration. A matrix with these characteristics makes        the subsequent treatment step more efficient, that is to say,        leaching in basic range, which dissolves the aluminium, in the        form of hydrated salt of an alkaline or alkaline earth metal,        together with some other compounds. At the end of the leaching        operations the solid has undergone a further concentration of        rare and rare earth metals, and, if necessary, passes to the        second concentrating step, alternative B.

The liquid obtained during the basic leaching contains mainly aluminiumin the form of hydrated salt of an alkaline or alkaline earth metal, butit also contains hydrated silica; this liquid is firstly treated withmilk of lime, to eliminate the silica; subsequently, the liquid istreated with CO₂. The buffering effect of the carbon dioxide brings thepH to a value such as to precipitate Al(OH)₃. The solid obtained in thisway is separated and calcined, producing Al₂O₃. The separated liquidreturns to the start of the alkaline leaching section, whilst theseparated hydrated silica is characterized in order to direct it to thecorrect recovery.

Second Concentrating Step (Alternative B), by Separating CompoundsContaining Aluminium and Silicon:

-   -   the slag exiting from the melting in the first concentrating        step is cooled to a temperature below 100° C. The material is        then finely ground, to maximize the specific surface area. The        particles must preferably have an average size of less than 0.2        mm.    -   The ground material passes to the subsequent leaching in acid;        the acid used is a diluted nitric acid solution, the        concentration of which must be at least 0.3 N, preferably 0.6 N.

The ratio (weight/volume) between the solid to be treated and the acidsolution is between 1/2 and 1/50.

The temperature of the system during the leaching is between 40° C. and95° C. at atmospheric pressure. The duration of the leaching reactiontime can range from 15 minutes to 120 minutes.

The solid separated at the end of the leaching reaction time can, ifnecessary, be subjected to a new leaching step, similar to the previousone.

In the reaction conditions, the solution extracts the rare and the rareearth metals present (plus the aluminium, the titanium and the otherelements present in smaller concentrations), whilst the majority of theiron present in the slag remains in the insolubilized residue; thelatter is separated from the acid leaching liquid, by known means, suchas, for example, decantation and filtration, and may be treated for theextraction of aluminium and silicon compounds, according to the methodsdescribed in the case of alternative A of the second concentrating step.

The liquid resulting from the acid leaching is sent, after filtration,to the next third concentrating step.

Third Concentrating Step, by Separating Compounds Containing Aluminium:

The liquid coming from the acid leaching, and which contains, insolution, rare and rare earth metals, as well as a not insignificantquantity of other elements, is treated on selective ion exchange resins,of cationic type.

The resins “capture” the rare and the rare earth metals present in thealkaline solution (such as, for example, scandium, yttrium andlanthanum), and block them on the active sites of the resin, therebyconcentrating them.

Together with the cations of the metals and rare metals, other cationsof any undesired elements present are also captured, if present.

The separation of the undesired elements is achieved by processing theresins with an extracting solution of HNO₃ with a concentration ofbetween 1.25 N and 1.75 N; in fact, with this concentration, only iron,aluminium, calcium, titanium and sodium are selectively brought intosolution, whilst the rare and rare earth metals of interest remainblocked on the resins.

Subsequently, by treating the resins with HNO₃ with a concentration ofbetween 3 N and 10 N, the rare and rare earth metals of interest areextracted and concentrated in acid solution, simultaneously regeneratingthe resins and making them available for a subsequent concentrationcycle on resins.

The acid solution contains an enriched mixture of rare and rare earthmeals, which can be selectively separated, according to one of the priorart techniques. By way of example, but without limiting the scope of theinvention, the extraction can be carried out with organic solvents suchas DEHPA (di-(2-ethylhexyl) phosphoric acid).

Concentrates of rare and rare earth metals are obtained with the processdescribed above.

The sole FIGURE appended shows the simplified block diagram of theinvention, in terms of its most extensive definition.

The description of the invention given above is of a general nature. Amore detailed description of a relative embodiment will now be given,with the help of the example, aimed at achieving a better understandingof the objects, features and advantages of the invention.

EXAMPLE

The example illustrate an application of the process according to theinvention.

A sample of red mud is dried to 250° C. and then ground. The followingtable shows the elementary analysis of the main elements of interestpresent on the sample of pre-treated red mud thus obtained, used in thisexample.

TABLE 4 Initial elementary analysis of the red mud used Unit ofParameter measurement Values Aluminium mg/kg 94,982.0 Iron mg/kg165,967.0 Yttrium mg/kg 52.0 Lanthanum mg/kg 83.0 Scandium mg/kg 40.0

First Concentrating Step:

during this step the aim is to drastically reduce, selectively, the ironcontent present in the matrix, both to obtain a concentration effect ofthe elements of interest, and because the iron is an importantinterfering element for the processes used in the subsequentconcentration and separation steps.

A basicity index corrector, containing silica and calcium oxide, isadded to the sample of red mud, suitably pre-treated. In this test, thebasicity corrector is added in order to obtain a binary basicity indexvalue IB₂ of approximately 0.6.

Moreover, an appropriate quantity of carbon is added, to give a suitablereducing potential to the load. A quantity of carbon equal to 11% of theweight of the sample of red mud is added in this test.

It should be noted that the quantity of the reducing agent and thebasicity index corrector added is determined, each time, on the basis ofthe red muds used.

The mixture formed by the pre-treated red mud, the basicity indexcorrector and the carbon is loaded in a plasma transferred arc reactor,in which the plasmogenic gas is nitrogen. The system must be maintainedin the reaction conditions, that is, at a temperature greater than 1300°C., until completion of the reduction reactions. In the case of thereactor used, this phenomenon occurred in approximately 60 minutes, butthis time may vary on the basis of the type of technology used to reachthe reaction conditions, the type of load (depending, for example, onthe content of iron oxides and interfering elements present), thegeometry of the reactor etc.

The slag and the pig iron produced are collected separately at the endof the reaction time. The slag, compared with the calcined red mud, is55% by weight; this means that the rare and the rare earth metals ofinterest, in the slag, should have a concentration of approximatelydouble, with respect to the pre-treated red mud. The following tableshows the elementary analysis of the main elements of interest presenton the sample of slag produced:

TABLE 5 Elementary analysis of the slag obtained after the firstconcentrating step Unit of Parameter measurement Values Aluminium mg/kg122,555.0 Iron mg/kg 24,877.0 Yttrium mg/kg 102.0 Lanthanum mg/kg 150.0Scandium mg/kg 80.0

As may be seen from the data shown in Table 4 and Table 5, theconcentration di Yttrium, Lanthanum and Scandium has almost doubledcompared with the sample of pre-treated red mud. As expected, thecontent of iron in the slag has considerably reduced, compared with thepre-treated red mud, falling from approximately 16.5% to approximately2.5%. The iron removed has resulted in a ferrous-based metallic phase(iron content>92%), which is similar to pig iron in terms of quality.The content of aluminium before and after the treatment has a lessregular trend, because the compounds containing this element alsoundergo reactions with the development of volatile compounds (flowmanaged separately and not included in the invention), so theconcentration factor of this element in the slag is approximately 30%.

Second Concentrating Step (Alternative B), by Separating CompoundsContaining Aluminium and Silicon:

-   -   the slag exiting from the melting in the first concentrating        step is cooled to a temperature below 100° C. Fine grinding of        the material is then carried out to obtain an average particle        size lower than 0.2 mm. In this way, the specific surface area        is maximized and the leaching reaction is improved. The ground        material passes to the subsequent leaching in acid; the acid        used is a diluted nitric acid solution, with a concentration of        0.6 N.

The ratio (weight/volume) between the solid and the acid liquid, used inthe test, was 1/50; the reaction system was also maintained at 90° C.and with atmospheric pressure.

At the end of the reaction time, the liquid was separated from the solidby mechanical decantation, by centrifuging; the clarified liquid wasthen filtered and analysed. The solid treated was recovered for anyextraction of aluminium and silicon compounds, according to the methodsdescribed in the case of alternative A of the second concentrating step.

The following table shows the percentage of extraction of the rare andrare earth metals of interest, calculated from the elementary analysisof these elements in the 0.6 N nitric acid solution, at the end of theleaching reaction:

TABLE 6 Elementary analysis of the 0.6N nitric acid solution, at the endof the leaching reaction Unit of Extraction after single Parametermeasurement passage (1 hour) Aluminium % 60.0 Iron % 22.5 Yttrium % 65.8Lanthanum % 18.7 Scandium % 50.0

The liquid resulting from the acid leaching is sent, after filtration,to the next third concentrating step.

Third Concentrating Step, by Separating Compounds Containing Aluminium:

the liquid coming from the acid leaching, and which contains, insolution, rare and rare earth metals, as well as a not insignificantquantity of other elements, is treated on selective ion exchange resins,of cationic type.

The resins “capture” the rare and the rare earth metals present in thealkaline solution (such as, for example, scandium, yttrium andlanthanum), and block them on the active sites of the resin, therebyconcentrating them. The concentration factor of the rare and rare earthmetals on the resins depends on the ratio between the volume of leachingliquid treated and the volume of the bed of selective resins. A typicalconcentration ratio is approximately 100 times.

The concentration ratio on the resins in the test in question was 20times. A volume of 2 litres of acid solution has been treated with avolume of 0.1 litres of selective resins.

Together with the cations of the metals and rare metals, other cationsof any undesired elements present, such as aluminium and iron, are alsocaptured, if present, in the test described.

The 0.6 N nitric acid solution, after the passage on resins, is sent tothe second step, for re-use in the process, if necessary with theaddition of new solution.

After having captured the rare and rare earth metals of interest,together with the undesired elements, the bed of selective resins, ofthe cationic type, is treated with a solution of nitric acid with aconcentration of between 1.25 N and 1.75 N. A nitric acid solution withthis concentration frees from the resin only the undesired elements,leaving the rare and rare earth metals on the bed.

The bed of selective resins is then washed with a nitric acid solutionwith a concentration of between 3 N and 10 N; in these conditions, therare and rare earth metals which were linked to the resins are removedfrom the bed. In this way, an acid solution is generated containing aconcentrate of a mixture of rare and rare earth metals. Theconcentration of the rare and rare earth metals in the resulting acidsolution depends on the content (in grams) of each element in thefiltering bed (degree of saturation of the filtering bed) and on theratio between the volume of the bed of resins and the total volume ofthe 3 N to 6 N nitric acid solution used. In the example in question,for instance, the 0.1 litre filter bed, containing 1.8 mg of scandium,has been washed with a volume of 0.5 litres of 6 N nitric acid solution,obtaining a concentration of 3.6 mg/litre of scandium in solution.

The rare and rare earth metals present in the nitric acid solutionobtained in this way can be separated selectively by means of one of theprior art techniques.

1. A process for the concentration of metals, rare metals and rare earthmetals, occurring in the powdery by-products resulting from thetreatment of bauxite (red mud) and transformation thereof intoindividual products to be used in the Bayer process and/or to be sent torespective reference markets thereof, comprising the following stages:First concentrating step, for the separation of occurring iron, whichessentially involves the following operations: Optional grinding anddrying of the material to be treated material at a temperature from 60to 250° C.; Optional roasting in order to eliminate also thecrystallization water; Optional grinding of the resulting product;Mixing with a component, capable of modifying the basicity index of themixture, called Fly Ash, that is a waste of other processes, so as toresult in a basicity index with values ranging from 0.1 to 2.0; Furthermixing with carbon-containing reducing substances to supplement thereducing action of the fly ash; Melting of the material in a firstreactor, with the operating temperature of melting bath≥1300° C.;Obtaining a product enriched in aluminium, titanium and other metals,rare metals and rare earth metals merging into the overlying slag fromwhich the underlying molten metallic product is separated in the form ofan iron alloy with minimum quality equal to pig iron; Secondconcentrating step, for separating the compounds containing aluminiumand silicon, which may involve a basic (alkaline) leaching or an acidleaching and, in the case of alkaline leaching, essentially comprisesthe following operations: Sending the molten slag, exiting from thereactor of the first concentrating step, into a second reactor where ata temperature of about 1000° C. an alkali and/or alkaline earth metalcarbonate is added to it and then it is cooled to temperature≤500° C.;Alkaline leaching of the resulting product in order for the aluminium tobe dissolved, in the form of hydrated salt of alkali and/or alkalineearth metal, and Si in the form of hydrated silica; Treatment of theliquid obtained with milk of lime in order to separate the silica andthen with CO2 to precipitate Al(OH)3 that is separated and calcined togive Al2O3; Sending the residual liquid into the head of the basicleaching section; Obtaining, at the end of the leaching operations, asolid having a higher concentration of the rare and rare earth metalcontent.
 2. The process according to claim 1, wherein the secondconcentrating step, in order to separate the aluminium and siliconcontaining compounds, and involving an acid leaching, essentiallycomprises the following operations: Cooling of the slag exiting from thereactor in the first concentrating step to a temperature below 100° C.;Fine grinding of the resulting product to maximize the specific surfacearea (average particle size lower than 0.2 mm); Acid leaching withaqueous solution of nitric acid 0.3 N, to extract rare and rare earthmetals along with the titanium and other possibly occurring traceelements, with separation of the unsolubilized residue from the acidleaching and treatment for the extraction of Al and Si compounds.
 3. Theprocess according to claim 2, where there is provided for a Thirdconcentrating step, which essentially comprises the followingoperations: Filtration of the liquid resulting from the acid leaching;Passage of the filtered liquid, which contains in solution rare, rareearth and undesirable metals, through selective ion exchange resins ofcationic type, on the active sites of which the cations of the abovemetals are blocked; Selective removal, from the resulting cationexchange resin, only of the undesired metals, such as iron, aluminium,calcium, titanium, sodium, with HNO3 aqueous solution of between 1.25 Nand 1.75 N; Subsequent extraction of the rare and rare earth metals fromthe cation exchange resin, deprived of the undesired elements, with HNO3aqueous solution of between 3 N to 10 N, resulting in the regenerationof the cation resin and use thereof in a subsequent concentrating cycle;Selective separation, by known techniques, from the resulting solution,of the individual extracted rare and rare earth metals.
 4. The processaccording to claim 1, wherein the basicity index of the mixture ischanged by Coal Fly Ash containing a significant carbon percentage and aresulting reducing activity.
 5. The process according to claim 1,wherein the first reactor for melting the material to be treated isselected from the group comprising reactors of the type EAF (ElectricArc Furnace), of the type plasma transferred arc, plasma not transferredarc, microwave plasma, Brown's gas reactor and electrolysis catalysedgas reactor.
 6. The process according to claim 2, wherein the acidleaching is performed with a ≥0.3 N, preferably 0.6 N, aqueous dilutednitric acid solution.
 7. The process according to claim 2, wherein theratio (weight/volume) between the material to be treated and the acidsolution is between 1/2 and 1/50.
 8. The process according to claim 2,wherein the temperature during the acid leaching is between 40° C. and95° C. at atmospheric pressure.
 9. The process according to claim 2,wherein the duration of the acid leaching is between 15 minutes and 120minutes.
 10. The process according to claim 2, wherein the acid leachingoperation is repeated at least once.
 11. The process according to claim2, wherein the unsolubilized residue is separated from the acid leachingliquid by the decantation or filtration technique.
 12. The processaccording to claim 2, wherein the selective removal, in the thirdconcentrating step, only of the undesirable metals is obtained bypassing through the cation exchange resin a nitric acid aqueous solutionfrom 1.25 N to 1.75 N.
 13. The process according to claim 2, wherein therare and rare earth metals are extracted, using a nitric acid aqueoussolution of from 3 N to 10 N, from the cation exchange resin, alreadydeprived of undesirable metals, which, being thus regenerated, isavailable for a subsequent resin concentration cycle.
 14. The processaccording to claim 2, wherein the solution enriched in rare and rareearth metals is subjected to known techniques for selective separationto obtain separately the individual components of the enriched solution.15. The process according to claim 14, wherein the selective separationis performed with organic solvents.
 16. The process according to claim1, wherein the organic solvent is DEHPA, di-(2-ethylhexil) phosphoricacid.
 17. The process according to claim 1, wherein the rare and rareearth metals to be concentrated are scandium, yttrium and lanthanum.